Synthesis and application of styrene/4-hydroxystyrene gradient copolymers made by controlled radical polymerization: Compatibilization of immiscible polymer blends via hydrogen-bonding effects

Styrene (S)/4-hydroxystyrene (HS) copolymers are synthesized by hydrolysis of S/4-acetoxystyrene copolymer precursors; two gradient copolymer precursors are made by semi-batch, nitroxide-mediated controlled radical polymerization, and a random copolymer precursor is prepared by conventional free radical polymerization. Conventional heat curves from differential scanning calorimetry indicate two glass transition temperatures (T_gs) and a broad T_g in well-annealed 59/41 mol% and 25/75 mol% S/HS gradient copolymers, respectively, both of which contain short S end-blocks. In contrast, a narrow T_g is observed in a 57/43 mol% random copolymer. Each S/HS copolymer is added at 5 wt% by solution mixing to an 80/20 wt% polystyrene (PS)/polycaprolactone (PCL) blend and tested for its ability to compatibilize the blend during melt processing; the hydroxyl groups on the HS units can form hydrogen bonds with the PCL ester groups. The S/HS random copolymer fails as a compatibilizer while both gradient copolymers are good compatibilizers. Relative to the blend without copolymer, the blend with 59/41 mol% S/HS gradient copolymer also exhibits a major reduction in initial dispersed-phase domain size and irregularly shaped domains, which are indicators of a sharply reduced interfacial tension. In contrast, the blend with 25/75 mol% S/HS gradient copolymer has an average PCL domain size comparable to the blend without copolymer and a broad domain size distribution. The presence of S/HS copolymers in the blend leads to reduced PCL crystallization and melting temperatures as well as reduced enthalpies of crystallization and melting, consistent with some solubilization of copolymer in the PCL domain interiors.     

复杂聚合物链结构的可控制备与新材料

自由基聚合与配位聚合的产物通常为宽分子量分布的均聚物或无规共聚物。近二十年来,活性/可控自由基聚合、活性/可控配位聚合、链穿梭聚合的研究取得突破。这些方法使得几乎所有的乙烯基单体,特别是廉价易得的单体,都可用作原料来制备原来无法制备得到的两嵌段、多嵌段共聚物、梯度共聚物等更为复杂聚合链结构。合理设计这些复杂的链结构,有望得到高性能、高附加值合成材料。介绍了这些新型聚合原理的机理、新进展,讨论了它们潜在的应用前景。     

Synthesizing and characterization of comb-shaped carbazole containing copolymer via combination of ring opening polymerization and nitroxide-mediated polymerization

The macro-TEMPO agent (poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl), PGTEMPO) was synthesized by anion ring-opening polymerization (ROP) of 4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (GTEMPO) using potassium t-butoxide as the initiator. The comb-shaped copolymer, PGTEMPO-g-PVBK, was prepared via nitroxide-mediated free radical polymerization (NMP) using PGTEMPO as macro-TEMPO agent and 9-(4-vinylbenzyl)-9H-carbazole (VBK) as the monomer. The polymerizations showed characteristics of “living”/controlled behavior. The optical properties, thermal analysis and electrochemical properties of the comb-shaped copolymers were investigated. The fluorescence and ultraviolet intensity and cyclic voltammetries of the comb-shaped copolymers with different molecular weight showed a regular order.     

Preparation of block copolymer particles by two-step atom transfer radical polymerization in aqueous media and its unique morphology

Submicron-sized poly(i-butyl methacrylate)-block-polystyrene particles were successfully prepared by two-step atom transfer radical polymerization (ATRP) in aqueous media: ATRP in miniemulsion (miniemulsion-ATRP) followed by ATRP in seeded emulsion polymerization (seeded-ATRP). When PiBMA particles, which were prepared by the miniemulsion-ATRP process with polyoxyethylene sorbitan monooleate (Tween 80, nonionic emulsifier) of 6-10 wt % based on iBMA, were used as seed in the seeded-ATRP of styrene, the block copolymer particles having narrow molecular weight distribution and pre-determined molecular weight were prepared at high conversion. Some block copolymer particles had an ‘onion-like’ multilayered structure. In this way, controlled/living free radical polymerization can be employed to obtain unique particle morphologies that may not be easily accessible using conventional free radical polymerization.     

TEMPO‐controlled radical suspension polymerization of poly(styrene)‐block‐poly(styrene‐co‐acrylonitrile) and poly(styrene)‐block‐poly(styrene‐co‐butyl methacrylate)

Suspension polymerization expands the study of controlled radical polymerization to high conversions and is known as a method to synthesize polymers with high molecular weights. The radical block copolymerizations of styrene (S) and acrylonitrile (AN) or butyl methacrylate (BUMA) controlled by 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) was performed in an oil/water pressure reactor system at a temperature of 125°C. TEMPO‐terminated styrene homopolymer was employed as macroinitiator. The systems were examined by varying the composition of the monomer mixture at a constant reaction time, as well as by varying the reaction time for a characteristic monomer composition to get all of the possible conversion range. The solubility effects of acrylonitrile in the suspension medium were considered. Furthermore, the yield of the reaction was improved through initiator addition by taking control of the reaction. The polymerizations could proceed under control up to a conversion of 80–90%. By using the copolymerization equations, the solubility of pure acrylonitrile in the suspension medium could be calculated and was found to be 8 wt.‐%.     

梯度共聚物的最新进展

阐述了梯度共聚物的概念及梯度共聚物的研究意义,介绍了梯度共聚物分类及特点,以及与这些特点相对应的各种用途。重点综述了近年来各种梯度共聚物的制备方法如常规乳液聚合、原子转移自由基聚合(ATRP)、可逆加成-断裂链转移聚合(RAFP)和氮氧调控自由基聚合(NMCRP)等,以及梯度共聚物的各种表征方法,如红外光谱(FT-IR)、核磁共振(NMR)、薄层色谱(TLC)以及X射线光电子能谱(XPS),并进一步分析了梯度共聚物的研究方向和研究重点。     

纤维素-g-PGMA接枝共聚物的可控合成

以棉纤维为原料,甲基丙烯酸缩水甘油酯(GMA)为单体,离子液体1-丁基-3-甲基咪唑氯盐(BMIMCl)为反应介质,采用原子转移自由基聚合法(ATRP)制备纤维素-g-PGMA接枝共聚物。通过FT-IR和GPC等仪器对产物结构进行了表征。动力学研究结果显示,GMA在离子液体中的ATRP聚合反应动力学呈一级反应动力学规律,并且相对分子质量随单体转化率呈线性增加,相对分子质量分布较窄,表明该聚合反应是活性可控的;合成的纤维素接枝共聚物在丙酮溶液中具有自组装行为。     

Synthesis and rheological properties of poly(styrene-co-butyl methacrylate) as an ink vehicle

Poly(styrene-co-butylmethacrylate) as an ink vehicle was synthesized using free radical polymerization. The molecular weights and monomer ratios in copolymers were determined. According to the results, the molecular weight could be controlled by the addition of a chain transfer agent and the copolymer ratio was nearly the same as the mole ratio of the monomer feed. The effect of the copolymer ratio on the rheological property was also studied. The polymer melt resembled a very viscous Newtonian fluid at a rate above the critical shear rate. Also, it is possible to synthesize a copolymer whose activation energy value is independent of the shear rate. The viscosity and melt behavior of the copolymer can be controlled with proper blending.     

Differences in enthalpy recovery of gradient and random copolymers of similar overall composition: styrene/4-methylstyrene copolymers made by nitroxide-mediated controlled radical polymerization

Styrene/4-methylstyrene (S/MS) random and gradient copolymers were synthesized by nitroxide-mediated controlled radical polymerization (NM-CRP) and compared to random copolymers made by conventional free radical polymerization (ConvFRP). The gradient copolymers have molecular weight (MW) values approaching 85,000 g/mol, making these some of the higher MW gradient copolymers reported to date. Due to the proximity of the glass transition temperatures (T_g) of polystyrene (PS) and poly(4-methylstyrene) (PMS), there is no significant difference in T_g between the gradient and random copolymers, with both copolymer types yielding single T_gs that typically increase slightly with increasing MS content. While enthalpy relaxation studies demonstrate similarity in random copolymers made by NM-CRP and ConvFRP, they reveal significant differences between random and gradient copolymers. Gradient copolymers exhibit broad enthalpy recovery peaks, whereas random copolymers exhibit narrower enthalpy recovery peaks. The maxima in the enthalpy recovery peaks are at substantially lower temperature, as much as 17 °C, in the gradient copolymers as compared to random copolymers of equal overall composition. While random and gradient copolymers of a given overall composition exhibit similar enthalpy recovery values at a common physical aging time and quench depth relative to T_g, the major differences in the enthalpy recovery peaks indicate that differences in sequence distribution along the chain length can lead to unusual behavior in gradient copolymers relative to random copolymers.     

Achievement of quasi-nanostructured polymer blends by solid-state shear pulverization and compatibilization by gradient copolymer addition

Nanoblends, in which dispersed-phase domains exhibit length scales of order 100 nm or less, are made using a continuous, industrially scalable, mechanical process called solid-state shear pulverization (SSSP). An 80/20 wt% polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend processed by SSSP and consolidated by platen pressing, without melt processing, exhibits a quasi-nanostructured morphology with many irregular, minor-phase domain sizes of ∼100 nm or less. After short-residence-time single-screw extrusion, the pulverized blend exhibits spherical dispersed-phase domains with a number-average diameter of 155 nm. Thus, SSSP followed by certain melt-processing operations can yield nanoblends. However, the pulverized blend exhibits significant coarsening of the dispersed-phase domains during long-term, high-temperature static annealing, indicating that SSSP followed by other melt processes may yield microstructured blends. In order to suppress coarsening, a styrene (S)/methyl methacrylate (MMA) gradient copolymer is synthesized by controlled radical polymerization. When 5 wt% S/MMA gradient copolymer is added to the PS/PMMA blend during SSSP, the resulting blend exhibits a nanostructure nearly identical to that of the blend without gradient copolymer, and coarsening is nearly totally suppressed during long-term, high-temperature static annealing. Thus, SSSP with gradient copolymer addition can yield compatibilized nanoblends. Morphologies obtained in the pulverized PS/PMMA nanoblend are compared with those in blends of PS/poly(n-butyl methacrylate) and PS/high-density polyethylene made using identical SSSP conditions, providing for commentary on the ability of SSSP to produce nanostructured blends as a function of blend components.     

Synthesis and characterization of pH/temperature-sensitive block copolymers via atom transfer radical polymerization

In order to prepare well-defined pH-sensitive block copolymers with a narrow molecular weight distribution (MWD), we synthesized a pH-sensitive block copolymer via atom transfer radical polymerization (ATRP) of sulfamethazine methacrylate monomer (SM) and amphiphilic diblock copolymers by the ring-opening polymerization of d,l-lactide/?-caprolactone (LA/CL), and their sol-gel phase transition was investigated. SM, which is a derivative of sulfonamide, was used as a pH responsive moiety, while PCLA-PEG-PCLA was used as a biodegradable, as well as a temperature sensitive one, amphiphilic triblock copolymer. The pentablock copolymer, OSM-PCLA-PEG-PCLA-OSM, was synthesized using Br-PCLA-PEG-PCLA-Br as an ATRP macroinitiator. The number average molecular weights of SM were controlled by adjusting the monomer/initiator feed ratio. The macroinitiator was synthesized by the coupling of 2-bromoisobutyryl bromide with PCLA-PEG-PCLA in the presence of triethyl amine catalyst in dichloromethane. The resultant block copolymer shows a narrow polydispersity. The block copolymer solution shows a sol-gel transition in response to a slight pH change in the range of 7.2-8.0. Gel permeation chromatography (GPC) and NMR were used for the characterization of the polymers that were synthesized.     

Compatibilized polymer blends with nanoscale or sub-micron dispersed phases achieved by hydrogen-bonding effects: Block copolymer vs blocky gradient copolymer addition

Addition of styrene (S)/4-hydroxystyrene (HS) block, blocky gradient, or blocky random copolymer to 80/20 wt% polystyrene (PS)/polycaprolactone (PCL) blends is examined as a compatibilization strategy. Four copolymers are synthesized by controlled radical polymerization, each with an S block and the other block being a HS block or S/HS random or gradient copolymer. Compatibilization depends on copolymer level and HS sequence distribution and content. Using a two-step solution-mixing/melt-mixing process, addition of 2 wt% and 5 wt% nearly symmetric S/HS diblock copolymer leads to compatibilization with average PCL domain diameters of 390-490 nm and 90-110 nm, respectively. In contrast, adding 0.25-0.75 wt% copolymer leads to microscale dispersed-phase domains and only reduced melt-state coarsening. Results with 2-5 wt% added copolymer indicate that a major reduction in interfacial tension is facilitated by hydrogen bonding of HS units and PCL carbonyl groups. Nanoscale confinement of normally semi-crystalline PCL within blends with 100 nm dispersed phases impedes PCL crystallizability, yielding liquid-state PCL domains at room temperature and demonstrating that properties of nanostructured blends and microstructured blends can differ greatly. Polystyrene/PCL blends are also made by one-step melt mixing with low mol% HS copolymers. Adding 5 wt% blocky gradient S/HS copolymer (86/14 mol% S/HS) leads to compatibilization with an average dispersed-phase diameter of 360-420 nm. In contrast, adding 5 wt% blocky random (87/13 mol% S/HS) or 5 wt% diblock (81/19 mol% S/HS) copolymer yields microscale dispersed-phase domains and only reduced coarsening. Crystallization in these blends is less hindered than in blends containing 2-5 wt% nearly symmetric S/HS diblock copolymer, indicating that both hydrogen bonding and confinement suppress PCL crystallization.     

ROP和ATRP法制备具有核壳结构的温敏性纳米胶束的研究

结合活性开环聚合(ROP)和原子转移自由基聚合(ATRP)方法,制备了以POSS-OH为核引发剂、PCL为核和PNIPAM为壳的X聚合物纳米胶束。借助GPC,IR,NMR,TEM,UV和DLS对聚合物的分子量、结构、形貌和温敏性进行了分析。结果表明,成功合成了星型嵌段共聚物;当POSS-OH的质量一定时,可以通过[CL]控制POSS-PCL的分子量;纳米胶束具有较为规整的球形和粒径分布均一;纳米胶束具有明显的温敏性与宽的相转变温度。     

Influence of the initiator system, cerium-polysaccharide, on the surface properties of poly(isobutylcyanoacrylate) nanoparticles

Isobutylcyanoacrylate has been used to form nanoparticles in presence of polysaccharides by two methods of polymerization. To have a better understanding of the relation between the structure of the resulting copolymer and the surface properties of the nanoparticles, the redox radical emulsion polymerization (RREP) was investigated and compared to anionic emulsion polymerization developed by Couvreur et al. (AEP Couvreur). The kinetic study showed that at pH1 the nanoparticles were formed in 5 min by RREP against 30 min in anionic emulsion polymerization (AEP pH1). The diameter of the nanoparticles was mainly affected by the concentrations of cerium and dextran and by the molecular weight of the dextran. The zeta potential was controlled by the characteristics of the polysaccharides (molecular weight and charge). The different methods of polymerization of isobutylcyanoacrylate led to nanoparticles with different surface properties.     

Facile fabrication of polyaniline/polypyrrole copolymer nanofibers with a rough surface and their electrorheological activities

Hierarchical polyaniline/polypyrrole (PANI/PPy) copolymer nanofiber was prepared via a two‐step method and adopted as dispersing materials for electrorheological (ER) fluids. The first step was used to synthesize PANI nanofibers by a rapid mixing method. Subsequently, the PANI/PPy copolymer nanofibers with a rough surface were obtained using an in situ polymerization method continuously. The morphology of the resultant PANI/PPy copolymer nanofibers can be controlled by varying the amount of Py monomer in the secondary in situ polymerization method. The rough surface of PANI/PPy copolymer nanofibers were confirmed by scanning electron microscopy and transmission electron microscopy. The diameter of PANI/PPy nanofiber is within the range 100–200 nm. The obtained PANI/PPy copolymer particles all exhibit amorphous structure through X‐ray diffraction measurement. We also demonstrated that the hierarchical PANI/PPy copolymer nanofibers exhibited characteristic ER behaviors, which were investigated using a Haake rotational rheometer at various electric field strengths. The ER efficiency e for PANI‐1mLPPy and PANI‐2mLPPy ER fluids at shear rate 0.1 s⁻¹ is 36.6 and 28.5 under electric field strength E = 3 kV/mm, respectively. Low leaking current density is observed even at high electric field strength and wide plateau region appeared, which show a strong ER activity for the PANI/PPy composite nanofibers. The results also indicate that the PANI/PPy composite particles have distinctly enhanced ER effect compared with the pure PANI and PPy particles under electric stimuli. The significantly improved ER property of PANI/PPy‐based ER fluid is ascribed to the enhanced interfacial polarization. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46289.     

Mechanical and thermal properties of an alternating methyl methacrylate styrene copolymer

The copolymer resulting from the polymerization of methyl methacrylate and styrene in the aqueous phase was tested for its mechanical and thermal properties. The usual procedure to obtain such a copolymer is by radical polymerization, but it can be done also by an ionic solution polymerization and in most cases the copolymer obtained has a statistical polymer arrangement. As this polymer is made by a complex mechanism in the presence of zinc chloride and water, it has many interesting features. The polymerization itself in the presence of water has a good industrial appeal as it simplifies considerably the operations as well as eliminates the suspension phase solvent cost. Another feature is the molecular weight distribution; we have two definite nearly monodisperse groups of polymers—one of these groups has an average molecular weight of 10⁷. The thermal properties of the polymers were studied as functions of the polymerization conditions and a mathematical expression was derived relating these factors. The mechanical properties of this, polymer compares favorably to available industrial products.     

Compatibilization efficacy of poly(isoprene–butyl acrylate) block copolymers in natural/acrylic rubber blends

Poly(isoprene–butyl acrylate) block copolymers with a variety of molecular weights and compositions were prepared via a controlled free‐radical polymerization with an iniferter. Subsequently, the block copolymers were used as compatibilizers in natural/acrylic rubber blends. Scanning electron micrographs revealed a cocontinuous morphology in the case of the normal blends with a low natural rubber content (20 wt %), whereas the blends that contained more natural rubber showed a dispersed‐particle morphology. When the rubbers were blended with 5 wt % block copolymer, the particle size decreased, and the tensile strength of the resulted blends increased, regardless of the block copolymer characteristics. For the blend that exhibited a cocontinuous morphology, the most effective compatibilizer was the block copolymer with an average molecular weight of 22,000 g/mol, containing mainly (87%) polyisoprene block. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 921–927, 2003     

Chemozymatic synthesis and characterization of H-shaped triblock copolymer

The synthesis of well-defined H-shaped block copolymer based on the enzymatic ring-opening polymerization (eROP) and atom transfer radical polymerization (ATRP) is described. The dihydroxyl polycaprolactone (PCL) was synthesized by the eROP of ε-caprolactone (ε-CL) in the presence biocatalyst Novozyme 435 and initiator ethylene glycol. Subsequently, the resulting PCL was converted to tetrafunctional macroinitiator by the esterification with 2,2-dichloro acetyl chloride (DCAC). The H-shaped block copolymer was then synthesized by the ATRP of styrene. The polymers were characterized by NMR and GPC. Linear first-order kinetics, linearly increasing molecular weight with conversion, and low polydispersities observed from the ATRP of St showed that the polymerization was well controlled. (PSt)₂-b-PCL-b-(PSt)₂ block copolymers with varying molecular weight and controllable composition were obtained.     

Preparation of amphiphilic PS-b-PMAA diblock copolymer by means of atom transfer radical polymerization

Amphiphilic diblock copolymers of polystyrene-b-poly(methacrylic acid) were synthesized by means of atom transfer radical polymerization. First, the polystyrene with a bromine atom at the chain end (PS-Br) was prepared using styrene as the monomer, 1-bromoethyl benzene as the initiator, and CuCl/2,2′-bipyridyl (bpy) as the catalyst ([1-bromoethyl benzene]/[CuCl]/[bpy] = 1:1:3). The polymerization was well controlled. Second, the diblock copolymer of polystyrene-b-poly(tert-butyl methacrylate) was synthesized also by atom transfer radical polymerization using PS-Br as the macro-initiator, CuCl/bpy as the catalyst, and tert-butyl methacrylate (tBMA) as the monomer. Finally, the amphiphilic diblock copolymer, PS-b-PMAA, was obtained by hydrolysis of PS-b-PtBMA under the acid condition. The molecular weight and the structure of aforementioned copolymers were characterized with gel permeation chromatography, infrared, and nuclear magnetic resonance. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2381–2386, 2001     

Synthesis of well‐defined comb‐like amphiphilic copolymers with protonizable units in the pendent chains: 1. Preparation of narrow polydispersity copolymers of methyl methacrylate and 2‐hydroxyethyl methacrylate by atom‐transfer radical polymerization

Well‐defined methyl methacrylate (MMA) and 2‐(trimethylsiloxy)ethyl methacrylate (Pro‐HEMA) copolymers were prepared by atom‐transfer radical polymerization(ATRP), using CuCl/2,2′‐bipyridine as catalytic system and p‐toluenesulfonyl chloride as initiator. ATRP process of MMA and Pro‐HEMA was monitored by ¹H NMR, and the kinetic curves of the MMA/Pro‐HEMA copolymerization were plotted in terms of the ¹H NMR data. At low content of Pro‐HEMA in the feed composition, the copolymerization can be well controlled with the molecular weight, polydispersity and the monomer distribution in the copolymer chain. With the increase of Pro‐HEMA content in the feed mixture, the composition of the final copolymer deviates from the composition of the feed mixture gradually, and gradient copolymers of MMA/Pro‐HEMA can be obtained. Through the hydrolysis process, well‐defined copolymers of MMA/HEMA were obtained from poly(MMA/Pro‐HEMA). Copyright © 2003 Society of Chemical Industry